Pilot stem



E. A. HALL PILOT STEM Aug. 6, 1935.

Original Filed April 28, 1928 19 v 6 14 1Q, 24 '23 Z 15 IT'EEE:

Patented Aug. 6, 1935 PATENT OFFICE PILOT STEM Ernest A. Hall, Toledo, Ohio, assignor to The Hall Manufacturing a corporation of Ohio Company, Toledo, Ohio,

Substitute for application Serial No. 273,501, April 28, 1928. This application July 14,1932,

Serial No. 622,414

2 Claims.

This invention relates to a pilot stem, of improved construction, adapted to be used in connection with valve seat grinders and other tools which operate in a similarmanner The present application is filed in substitution of an application Serial No. 273,501, filed April 28, 1928. The object of the invention is to provide, for the purpose stated, a pilot stem or spindle which is so constructed that it may be easily and firmly secured in a valve stem guideway, and in connection therewith, to provide improved means for adjusting and centering the lower end portion of the stem within the guideway.

In using pilot stems, as heretofore commonly constructed, for the purpose of centering valve seat grinders and the like, it has been necessary to secure the pilot stem in proper position by applying a centering nut, expanding screw or equivalent means to the lower end ofthe stem after it has been inserted in the valve rod guideway. With the present invention, the entire pilot stem and adjusting means may be first assembled and then inserted through the upper end of the guideway, and after it has been thus inserted, the lower end may be easily adjusted and centered with respect to the guideway and the entire stem is held securely in correct position, even though the upper and lower ends of the guideway are considerably Worn. I The specific construction of the invention and the advantages resulting therefrom will be more particularly described in connection with the accompanying drawing, in which:-

Fig. 1 is a vertical section taken centrally through the lower part of the valve seat grinding tool and the adjacent portion of the motor, with the pilot stem secured in operative position.

Fig. 2 is an enlarged fragmentary section showing the expansible collet and expanding member in fully expanded position, the section being taken on line 22 of Fig. 3.

Fig. 3 is a detail plan view of the collet.

The internal combustion motor, a fragment of which is shown at 5,-is formed with a cavity 6 which may represent a part of either the inlet or than the diameter of the guideway 8 and is formed at its lower end with a reduced portion M which is threaded to receive an extension l5 which is formed at its upper endwith a correspondingly threaded bore I6.

The body portion l3 of the stem is formed intermediate its ends with a downwardly facing conical enlargement H, the base of which is somewhat larger than the internal diameter of the guideway 8. At the point where the main portion of the stem |3 merges into the reduced portion [4, it is formed with a downwardly facing uniformly tapered portion l8 which is adapted to receive a collet 2|. The dimensions of the stem are such that when the conical enlargement I1 is seated in the'upper end of the guideway 8 the tapered portion I8 is located within the guideway near the lower end thereof and the extension I5 projects below the end of the guideway.

The normal outside diameter of the collet 2| is slightly less than the diameter of the guideway 8 so that it may be easily inserted therein. The inner surface of the collet is tapered to correspond to the tapered surface l8. The collet has one side split, as shown at 22, so that as it is forced upwardly on the tapered surface |8 it will be expanded and will be forced with increasing pressure against the wall of the guideway.

Longitudinal grooves 23 and 24 are provided on the internal surface of the collet to permit an equal and easy expansion of this member.

When the pilot stem I3, the extension l5 and the collet 2| are assembled, the extension I5 is screwed onto the reduced portion l4 sufiiciently to retain the collet on the stem, but not far enough to expand the collet. When thus assembled, the stem may be inserted from the upper end of the guideway 8 and. forced downwardly until the tapered enlargement I1 is firmly seated inthe upper end of theguideway. The extension I5 is then screwed up, forcing the collet upwardly over the surface l8, thus expanding the colletand causing it to bear forcibly against the wall of the guideway. At the same time the resistance of the collet against thewall of the guideway causes the stem to be drawn more firmly against its seat.

In order to facilitate the insertion of the pilot stem and the adjustment of the collet to center the lower end thereof, transverse holes 25 and 26 are formed in the upper and lower ends respectively, for receiving cross rods.

The provision of the grooves 23 and 24 in the inner surface of the collet 2| facilitates the expansion of the collet. These grooves extend from end to end of the collet and their bottoms are parallel to the periphery thereof.

In the expansion of the collet the outer surface will always maintain a substantially cylindrical shape. If the lower end of the guideway is enlarged by wear and is even elliptical in shape, the expanded collet will nevertheless effect a true centering of the pilot stem.

The depth of the bore l 6 is so gaged that it will act as a stop in screwing up the extension 55, before the expansion of the collet reaches its elastic limit, so that under no circumstances can the collet be accidentally broken by adjusting it too far.

After inserting the pilot stem in the guideway, it is not necessary to attach any nut, screw or the like to its lower end. All that it is necessary to do is to tighten the lower extension l5 by hand or by means of a cross rod inserted through the hole 25.

When the grinding of the valve seat has been completed, the extension 85 may be loosened sufficiently to permit the collet to work downwardly, or for the stem to work upwardly and permit the collet to contract and disengage the wall of the guideway.

In the use of a pilot stem of the class described it is highly important that the stem be truly centered with respect to the valve seat to be ground; otherwise an improper grinding is effected. Such centering is diflicult to obtain, especially when the stem is used in connection with a worn valve stem guide, which condition is usually present to a greater or less extent where valve reseating is necessary. The wear occasioned in the guide usually effects a gradual enlarging of the guide from the centers outwardly in both directions and is also frequently elliptical or out-of-round in cross-section. It is, therefore, necessary to provide the pilot stem with guide engaging means which, when tightened, will cooperate with the guide to effect a true centering of the stem with respect to the valve seat. It is apparent that, if the lower end of the stem is so held that it is only one or two thousandths of an inch out of true centering alinement with the guide opening, this will effect a considerably greater error in the centering of the upper end of the stem with respect to the valve seat. It is, therefore, important to have the engaging means of such a character as to center the stem as nearly without any error in alinement as is possible. It is apparent that, if the stem does not aline accurately with the center of the valve seat, the grinding tool, which is guided by the stem, will effect a greater cutting of material from the valve seat at one side of its center than the other.

It is found in practice that with the use of an expansible collet on the taper l8 of the stem, in conjunction with means for forcing the collet upward on the taper to effect the expanding action, a very accurate and effective centering of the pilot stem with respect to the guide is accomplished. It is also found that such centering is rendered more accurate and positive irrespective face as is possible and at the same time permit the expanding action. Without this substantially continuous annular guide wall engaging sur face of the expanding member, it is found practically impossible to obtain the same setting of a pilot stem twice in the same guide opening, particularly where the opening is slightly outof-round, so that the stem when secured in the guide at one time would be off center in a different direction from that which it would assume when secured in the guide at another time. By the use, however, of a split ring form of collet, as herein described, it is possible to secure the same setting of the stem with any guide opening each time it is mounted therein.

While I have shown and described specifically one form in which the invention may be embodied, it is apparent that the details of the same may be modified in some respects without departing materially from the scope of the invention as claimed.

What I claim is:

1. The combination with a pilot stem adapted to be inserted in a valve stem guideway, of means cooperating with the upper end of the guideway to center the upper part of the stem, a reduced tapered portion formed on said stein near its lower end, an expansible collet having a substantially continuous tapered internal face cooperating with t e tapered portion of said stem, said collet having a plurality of weakened portions on its said internal face spaced inwardly of its periphery whereby to equalize the expansion of said collet, and means connected to the stem to expand said collet by forcing the tapered portionof said collet into engagement with the tapered portion of the stem.

2. The combination with a pilot stem adapted to be inserted in a valve stem guideway, of means cooperating with the upper end of the guideway to center the upper part of the stem, a reduced tapered portion formed on said stem near its lower end, an expansible collet having a substantially continuous tapered internal face cooperating with the tapered portion of said stem, said collet having a plurality of axially extending grooves on its said internal face which extend through each of its ends and the bottoms of which are parallel to and spaced inwardly of the periphery of the collet whereby to equalize the expansion ofthe collet, and means connected to the stemto expand said collet by forcing the tapered portion of said collet into engagement with the tapered portion of the stem.

1 ERNEST A. HALL. 

